Damage mitigation for gearbox

ABSTRACT

A component of a rotary wing aircraft is provided including a surface configured to contact another component of the rotary wing aircraft such that the surface is susceptible to corrosion and/or pitting. The surface has an area from which a portion of material was removed. A structural deposit is formed by cold spraying one or more layers of powdered material within the area. The structural deposit is configured to carry a load applied to the component.

BACKGROUND OF THE INVENTION

Exemplary embodiments of the invention relate to components of arotary-wing aircraft susceptible to corrosion damage and, moreparticularly, to a method for preventing or reducing corrosion damage tosuch a component of a rotary-wing aircraft.

A rotary-wing aircraft includes components, such as gearboxes forexample, typically constructed from aluminum and magnesium alloys. As aresult of exposure of such components to the environment, these alloymaterials are susceptible to both general corrosion and galvaniccorrosion. For example, the presence of water or moisture on the outersurface of the component may cause corrosion and other environmentalconditions, such as chemical fallout and saltwater for example, mayexacerbate corrosion. Alternatively, electro-chemical incompatibilitywith adjacent components can lead to galvanic corrosion. Both corrosionmodes cause the material of the component to deteriorate, therebyreducing the cross-section thickness thereof. In some instances, thecomponent's effective cross-section may be excessively reduced such thatthe structural integrity of the component is compromised.

Conventional rotary-wing aircraft component repair methods allow fordimensional restoration of aluminum and magnesium structures using avariety of techniques including, but not limited to, epoxy bonding,plasma spray, high velocity oxygen fuel (HVOF) thermal spray and fusionwelding for example. High temperature repair techniques may result inunacceptable component distortion and degrade the substrate materialproperties by over-aging or solutioning. Epoxy bonding can break orspall during service, allowing the environmental elements to attack theunderlying material. Subsequent attacks on the material will deterioratewall thickness such that the component is no longer usable. In addition,none of these repair methods result in the formation of a depositsuitable for carrying a load.

BRIEF DESCRIPTION OF THE INVENTION

According to one embodiment of the invention, a component of a rotarywing aircraft is provided including a surface configured to contactanother component of the rotary wing aircraft such that the surface issusceptible to corrosion and/or pitting. The surface has an area fromwhich a portion of material was removed. A structural deposit is formedby cold spraying one or more layers of powdered material within thearea. The structural deposit is configured to carry a load applied tothe component.

According to another embodiment of the invention, a method of rebuildinga damaged portion of a surface of a component is provided includedforming an area in the surface by removing all material exhibitinglocalized corrosion and/or pitting and preparing the formed area. Astructural deposit is created in the area and is integrally formed withthe component. The structural deposit is configured to carry a loadapplied to the component. Excess material is removed from the structuraldeposit.

According to another embodiment of the invention, a method ofpreemptively forming a structural deposit in a surface of a component isprovided included identifying a portion of the surface where damage isexpected to occur to form an area. The identified portion is thenprepared. A structural deposit is created in the identified portion andis integrally formed with the component. The structural deposit isconfigured to carry a load applied to the component. Excess material isremoved from the structural deposit.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of an exemplary rotary wing aircraft;

FIGS. 2a and 2b are exemplary schematic diagrams of the main rotorsystem and the tail rotor system of the aircraft of FIG. 1;

FIG. 3 is a perspective view of a gearbox housing of a rotary wingaircraft according to an embodiment of the invention;

FIG. 4 is a perspective view of a mating surface of a gearbox housing ofa rotary wing aircraft according to an embodiment of the invention;

FIG. 5 is a cross-sectional view of a portion of a gearbox housinghaving an integrally formed structural deposit according to anembodiment of the invention;

FIG. 6 is a method for rebuilding a portion of a surface of a gearboxhousing according to an embodiment of the invention; and

FIG. 7 is a method for preemptively forming a structural deposit in asurface of a gearbox housing according to an embodiment of theinvention.

The detailed description explains embodiments of the invention, togetherwith advantages and features, by way of example with reference to thedrawings.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically illustrates a rotary-wing aircraft 10 having a mainrotor system 12. The aircraft 10 includes an airframe 14 having anextending tail 16 which mounts a tail rotor system 18, such as ananti-torque system, a translational thrust system, a pusher propeller,or a rotor propulsion system for example. Power is transferred from oneor more engines E to a power transmission gearbox 20 (see FIGS. 2a and2b ), to drive the main rotor system 12 about a respective axis ofrotation A. Although a particular rotary wing aircraft configuration isillustrated and described in the disclosed embodiment, otherconfigurations and/or machines, such as a high speed compound rotarywing aircraft with supplemental translational thrust systems, a dualcontra-rotating, coaxial rotor system aircraft, and a turbo-prop,tilt-rotor or tilt-wing aircraft for example, will also benefit from thepresent invention.

Referring now to FIG. 2a , a schematic diagram of the main rotor system12 and the tail rotor system 18 of the aircraft 10 of FIG. 1 is providedin more detail. In the illustrated non-limiting embodiment, the powertransmission gearbox 20 is interposed between one or more engines E, themain rotor system 12 and the tail rotor system 18. The gearbox 20 may bemechanically connected to and configured to operate both the main rotorsystem 12 and the tail rotor system 18. In another embodiment, shown inFIG. 2b , the rotary wing aircraft 10 includes a first powertransmission gearbox 20 mechanically coupled to and configured tooperate the main rotor system 12. Similarly, the second powertransmission gearbox 21 is mechanically connected to and configured tooperate the tail rotor system 18. Each of the power transmissiongearboxes 20, 21 receives power from at least one engine E of theaircraft 10.

The power transmission gearbox 20, 21 is generally mounted within ahousing 22 configured to support the gear-train therein. In oneembodiment, the housing includes either an aluminum or a magnesiummaterial. The non-limiting embodiment of a housing 22, illustrated inFIG. 3 generally includes a plurality of first openings 24 configured toprovide a plurality of passageways for a lubricant to various portionsof the gearbox 20. The housing 22 may also include a plurality of secondopenings 26 configured to at least partially support an input moduleattachment (not shown), such as the rotor shaft (not shown) of the mainrotor system 12 or the tail rotor system 18 for example. In addition,the housing 22 may include a plurality of mounting feet 28 arrangedabout the periphery thereof near a first end 23. Although a particulargearbox housing 22 configuration is illustrated and described in thedisclosed non-limiting embodiment, other configurations are within thescope of the invention.

The portions of the housing 22 that are most susceptible to damage, aswell as corrosion and pitting are generally the surfaces 30 configuredto contact or engage another component and/or a material distinguishablefrom the material of the housing 22. Exemplary surfaces 30 include, butare not limited to, end mating surface 30 a, flight control surfaces 30b, and bottom surfaces 30 c for example. The end mating surface 30 a islocated at the first end 23 of the housing 22 and is configured toengage a portion of the airframe 14 or another component of the aircraft10. As illustrated in FIG. 4, at least one fastener 32 may extendgenerally perpendicularly from the end mating surface 30 a, the at leastone fastener 32 being configured to connect the first end 23 of thehousing 22 to another portion of the aircraft 10. Each flight controlsurface 30 b is configured to couple to a flight control or anothercomponent (not shown) of the aircraft 10. A plurality of flight controlsurfaces 30 b may be disposed about the exterior of the housing 22 andmay be arranged at any angle relative to the end mating surface 30 a.Similarly, the bottom surfaces 30 c are the portion of the mounting feet28, such as the underside for example, configured to contact anothercomponent of the aircraft 10 or a portion of the airframe 14.

Referring now to FIG. 5, a structural deposit 40 configured to support aload applied to the housing 22 is formed on at least a portion of asurface 30 of the gearbox housing 22 susceptible to corrosion andpitting. The structural deposit 40 may be formed from any suitablepowdered material known in the art, such as aluminum or aluminum alloyfor example. In one embodiment, the structural deposit 40 is formed as ameans of repairing the housing 22 after either external damage (i.e.nicks, dings or gouges) or corrosion and/or pitting has alreadyoccurred. In another embodiment, the structural deposit 40 is formed asa “preemptive repair” based on a determination of where corrosion andpitting is most likely to occur.

A structural deposit 40 is formed by applying one or more layers ofpowdered material to an area 42 of the surface 30. In embodiments wherethe structural deposit 40 is applied after corrosion has occurred, eacharea 42 is created by removing as little of the material of the surface30 as necessary to completely eliminate all of the localized corrosionand pitting. Some of the adjacent non-compromised material of thesurface 30 may additionally be removed along with the localizedcorrosion and pitting to ensure that the remaining material of thehousing 22 has not been compromised. In embodiments where the structuraldeposit 40 is applied “preemptively,” each area 42 is created either byremoving material from the surface 30 where corrosion and pitting aremost likely to occur, or by depositing one or more layers of powderedmaterial used to form a structural deposit 40 on top of the as-processed(or as-cast) surface. In either embodiment, the one or more areas 42formed in the surface 30 are generally, but not limited to, concavegrooves.

The one or more layers of powdered material used to form the structuraldeposit 40 are more substantial than a coating and are configured toshare a load applied over the surface 30. As a result, the strength of ahousing 22 having one or more structural deposits 40 integrally formedwith the surfaces 30 where corrosion and pitting has/is likely to occuris near, substantially equal to, or in excess of the original strengthof the housing 22. The structural deposit 40 formed from one or morelayers of powdered material may have a thickness in the range of about0.010 inches and 2.00 inches. In one embodiment, the structural deposit40 has a thickness greater than or equal to 0.025 inches, depending onpart geometry and other factors, to properly share the load applied tothe component.

The layers of powdered material used to form the structural deposit 40are generally applied through a deposition process that providessufficient energy to accelerate the particles to a high enough velocitysuch that the particles plastically deform and bond to the area 42 uponimpact. The particles of the powered material are accelerated through aconverging/diverging nozzle 52 of a spray gun 50 to supersonicvelocities using a pressurized or compressed gas, such as helium,nitrogen, other inert gases, or mixtures thereof. The deposition processdoes not metallurgically transform the particles from their solid state.Various techniques may be used to achieve this type of particledeposition, including but not limited to, cold spray deposition, kineticmetallization, electromagnetic particle acceleration, modified highvelocity air fuel spraying, or high velocity impact fusion (HVIF) forexample.

The layers of powered material may be applied to the original materialof the housing 22, or alternatively, may be applied to a previouslyformed structural deposit 40. During deposition of the powderedmaterial, the gearbox housing 22 may be held stationary or may bearticulated or translated by any suitable means (not shown) known in theart. Alternatively, the nozzle 52, of the spray gun 50 may be heldstationary or may be articulated or translated. In some instances, boththe gearbox housing 22 and the nozzle 52 may be manipulated, eithersequentially or simultaneously.

A method 100 for rebuilding a damaged or corroded portion of a surface30 of a gearbox housing 22 is illustrated in FIG. 6. The surface 30 maybe any of the surfaces 30 a, 30 b, 30 c previously described. The methodbegins in block 102 by removing all of the localized damage or corrosionfrom a portion of surface 30 to form an area 42 (see FIG. 5). Thecorrosion and pitting may be removed either mechanically or chemically,for example using grinding, machining, etching, or other applicabletechniques. After the localized corrosion is removed, as shown in block104, the surface 30 is prepared and masked as is known in the art. Inone embodiment, preparation and masking of the surface 30 involves theuse of an abrasive grit blast. An additional material may be used toeliminate any blast residue as a course of contamination prevention. Inblock 106, at least one layer of powdered material is applied to thearea 42 using a cold spray deposition process to create a structuraldeposit 40 integrally formed with the material of the housing 22. Thestructural deposit 40 bonded to the area 42 may extend beyond theoriginal dimension of the surface 30 of the gearbox housing 22. Afterformation of the structural deposit 40, excess material is removed asnecessary, as shown in block 108. As a result, the structural deposit 40is generally flush with the remainder of the surface 30 of the gearboxhousing 22 and/or the dimension of the gearbox housing 22 including thestructural deposit 40 is substantially equal to the original dimensionthereof.

A method 200 of preemptively forming a structural deposit 40 in asurface 30 of a housing 22 is illustrated in FIG. 7. The surface 30 maybe any of the surfaces 30 a, 30 b, 30 c previously described. The method200 may begin in block 202 by removing some material from the surface 30of an unused gearbox housing 22, at a position where localized corrosionand pitting is most likely to occur, to form an area 42. Material may beremoved from the surface 30 either mechanically or chemically, forexample using grinding, machining, etching, or other applicabletechniques. In embodiments where a structural deposit 40 is being addedto the existing surface of the housing 22 without first removing anymaterial, the step illustrated in block 202 may be skipped. In block204, the portion of the surface 30 configured to receive the structuraldeposit 40, such as area 42 for example, is prepared and masked, aspreviously discussed. In block 206, at least one layer of powderedmaterial is applied using a cold spray deposition process to form astructural deposit 40. The structural deposit 40 bonded to the surface30 may extend beyond a desired dimension, such as the original dimensionof the surface 30 of the gearbox housing 22 for example. In suchinstances, excess material is removed after formation of the structuraldeposit 40, as shown in block 208. The excess material 40 may be removedso that the structural deposit 40 is generally flush with the remainderof the surface 30 of the gearbox housing 22 so that the dimension of thegearbox housing 22 including the structural deposit 40 is substantiallyequal to the original dimension thereof.

Formation of one or more structural deposits 40 in the surfaces of agearbox housing 22 can reduce and/or prevent corrosion and pitting,thereby improving the life of the housing 22. In addition, because thestructural deposits 40 are configured to share the load applied to thesurface 30, inclusion of one or more structural deposits 40 does notaffect or minimally decreases the structural integrity of the housing22.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

The invention claimed is:
 1. A method of rebuilding a damaged portion of a surface of a gearbox housing, the surface configured to engage with and support a load of a portion of an aircraft, the method comprising: forming an area in the surface by removing all material exhibiting at least one of localized damage, corrosion and pitting; preparing the area; creating a structural deposit in the area, the structural deposit being integrally formed with the gearbox housing, and the structural deposit configured to share the load applied to the gearbox housing by the portion of the aircraft; and removing excess material from the structural deposit.
 2. The method according to claim 1, wherein the gearbox housing is configured for a rotary wing aircraft and the portion of the aircraft is a portion of the rotary wing aircraft.
 3. The method according to claim 1, wherein the structural deposit includes one or more layers of powdered material applied to the area through a cold spray deposition process.
 4. The method according to claim 3, wherein the powdered material includes aluminum.
 5. The method according to claim 1, wherein the excess material is removed so that the structural deposit is substantially flush with the surface.
 6. The method according to claim 1, wherein the excess material is removed so that a dimension of the component including the structural deposit is substantially equal to an original dimension of the component.
 7. A method of preemptively forming a structural deposit on a non-corroded surface of a first component, the surface configured to engage with and support a load of a second component, the method, comprising the steps of: selecting an unused gearbox housing as the first component; identifying a portion of the non-corroded surface of the gearbox housing where at least one of corrosion and pitting is expected to occur; removing material from the portion of the non-corroded surface of the gearbox housing; preparing the portion of the surface; creating a structural deposit on the portion of the surface identified where at least one of corrosion and pitting is expected to occur, the structural deposit being integrally formed with the first component, and the structural deposit configured to share the load applied to the first component; and removing excess material from the structural deposit.
 8. The method according to claim 7, wherein selecting the gearbox housing includes selecting a gearbox housing of a rotary wing aircraft.
 9. The method according to claim 7, wherein the structural deposit includes one or more layers of powdered material applied through a cold spray deposition process.
 10. The method according to claim 9, wherein the powdered material includes aluminum.
 11. The method according to claim 7, wherein the excess material is removed to achieve a desired dimension.
 12. The method according to claim 11, wherein the desired dimension is substantially equal to an original dimension thereof.
 13. The method according to claim 7, wherein the surface is one of a mating surface, a flight control surface, and a mounting foot portion, and the second component is one of a fastener, a flight control component, and an airframe.
 14. A method of preemptively forming a structural deposit on a non-corroded surface of a first component, the surface configured to engage with and support a load of a second component, the method, comprising the steps of: selecting an unused gearbox housing as the first component; identifying a portion of the non-corroded surface of the gearbox housing where at least one of corrosion and pitting is expected to occur; creating a structural deposit on the portion of the surface identified where at least one of corrosion and pitting is expected to occur by adding the structural deposit to the surface without first removing material from the portion of the surface, the structural deposit configured to share the load applied to the first component; and removing excess material from the structural deposit. 